In the prior art, air feed pipe lines laid in a factory are grouped into two systems consisting of high-pressure air feed pipe lines and low-pressure air feed pipe lines, respectively, and these air feed pipe lines are introduced to various kinds of machines disposed in the factory to be utilized as drive power sources.
In addition, in the air fed through the air feed pipe lines in mixed lubricating oil, and by lubricating a slide portion of an actuator with this lubricating oil, smoothening of the operation of the actuator and prevention of abrasion of the slide portion are contemplated, but in the prior art, for instance as shown in FIG. 1, a lubricating oil injection device b is provided only in a low-pressure side air feed pipe line a, and lubricating oil is injected only to the side of the low-pressure air feed pipe line.
In the above-described lubricating system in the prior art, in the case where it is intended to inject lubricating oil also to a high-pressure side air feed pipe line c, a pipe line d connecting the low-pressure side air feed pipe line a with the lubricating oil injection device b, is connected to the high-pressure side air feed pipe line c through a pipe line e to introduce the pressure in the high-pressure side air feed pipe line c into the lubricating oil injection device b, and further, unless this introduced pressure is enhanced by a booster f, the air injected with the lubricating oil cannot be returned to the high-pressure side air feed pipe line c.
However, in the event that the high-pressure side air feed pipe line c and the pipe line d leading to the lubricating oil injection device b are connected through the pipe line e, the high-pressure side air would flow into the low-pressure side, resulting in a disadvantage that the pressure in the high-pressure side air feed pipe c is lowered.
Therefore, in the lubricating system in the prior art, the lubricating oil injection device b had to be provided for each of the high-pressure side air feed pipe line c and the low-pressure side air feed pipe line a, and so, there was inconvenience that the expense became large, and also a lot of space was necessitated for installing two sets of lubricating oil injection devices b.